The present invention relates to plumbing fittings which join together opposed ends of broken or otherwise dissimilar pipe segments using compressive forces, and more specifically to a plumbing compression fitting which is used by municipalities and commercial plumbing contractors for coupling free ends of water supply pipes.
Compression fittings of the sort contemplated by the present invention are typically used when connecting the water line of a new construction, i.e., a new or remodeled residence or commercial building, with pipes from an existing water system. In many cases, the new construction employs copper pipe, while the pipes of the existing water system are galvanized steel, cast iron or even lead, depending on the age of the system. Since ends of the copper pipe are too soft to support threads, the common method of attachment is to solder together the ends of adjacent copper pipe segments using socket type fittings. However, segments of non copper (galvanized, iron or lead) pipe are typically threaded together using various couplings, nipples, tees, etc. as are well known in the art. A problem arises when repairs are required in existing water systems using non copper pipe, or in construction situations where a copper line has to be connected to an existing non copper pipe system. In some cases, the existing non copper system has ruptured and there are free ends of pipe to be joined using segments of replacement pipe.
Compression fittings are known for use in coupling copper pipe to non copper pipe. Such fittings typically include a main housing which is constructed along the axis of the two pipe ends to be joined. After threading a capture nut and a compression ring over the end of each pipe to be coupled, each pipe end is inserted into an opposite end of the main housing. Regarding the non copper pipe end, which is typically cut to have a straight end, the capture nut receives the compression ring and is then threaded onto the end of the main fitting housing. As the capture nut tightens upon the housing, the compression fitting is compressed and simultaneously seats upon the end of the fitting, and is compressed to form a tight interference fit between the capture nut and the pipe. In some applications, the capture nut is castellated, and employs a set screw or locking pin to hold the nut in place.
On the copper pipe side of the fitting, the end of the copper pipe is typically flared after threading a capture nut thereon. The capture nut has a corresponding flared contour, and as the nut is tightened upon the opposite end of the housing, the flared pipe end is pressed into abutting relationship against a radiused or contoured end of the fitting which corresponds to the flare of the pipe. Further tightening of the capture nut creates a tight seal of the flared pipe end against the housing, usually without the use of a separate compression ring.
These types of fittings are conventionally available in embodiments designed for household use and/or for contractor use in coupling the water systems of buildings to main water feed lines, and for repairing large sections of existing water systems. However, the present invention is primarily concerned with compression fittings of the type used by contractors. One problem with conventional compression fittings of this type, is that on the non copper pipe end of the main compression fitting housing, a plastic or polymeric compression ring is used. A drawback of this type of component is that upon extreme tightening to obtain a water tight seal, the plastic compression ring can be deformed to the extent that it is partially forced out the back of the capture nut. Even when such assemblies obtain a water tight seal, the coupling cannot be reused if subsequent repairs to that section of pipe are needed. Similar disadvantages have been observed with compression rings made of metal.
Another drawback of conventional compression couplings is that when the existing pipe is made of lead, in the course of repairing and reinstalling the water line in the ground, the pipe often is subject to an axial pulling force which causes the pipe to be pulled out of the coupling. The pulling force may be due either to contractor's activities or to natural ground movements. Since this reopens the leak just repaired, it is obviously a situation to be avoided. A related drawback concerns the constitution of the lead pipe. It has been found that upon over tightening of conventional compression fittings at repair junctions of lead pipe, the lead pipe has been known to compress to the point that the inner diameter of the pipe narrows or "necks down". This situation may cause unwanted pressure variations and resulting stresses on the water system.
Still another disadvantage of conventional copper/non copper pipe compression fitting connections is that in some cases, the copper and lead pipe come in contact with each other, which causes galvanic corrosion and further weakens aging water systems.
Yet another drawback of conventional compression fittings is that when the castellated capture nuts and set screws are employed, in some cases the contractor does not adequately tighten the set screw, or completely forgets to tighten it at all. Eventually the nut works lose and the coupling begins to leak.
Thus, there is a need for a plumbing compression fitting which can couple copper to non copper pipes in a way that water tight seals are achieved. There is also a need for such a fitting which can be reopened upon the need for subsequent repair, and which allows the reuse of the compression fitting components. Further, there is a need for an improved fitting which does not cause lead pipe to neck down upon tightening.
Accordingly, a first object of the present invention is to provide an improved compression fitting which maintains a water tight coupling upon axial pulling force exerted on the coupled pipe.
Another object of the present invention is to provide an improved compression fitting in which the compression member does not deform under tightening and is reusable.
A further object of the present invention is to provide an improved compression fitting which does not cause necking down of lead pipe upon tightening.